The physiology of human auditory perception is highly adaptive. So we get used to what we listen to regularly. Theoretically, in the electronics, including crossovers, some time might be required to polarise electrolytic capacitors. This should not take too long unless they are deteriorated. Again, the mechanical parts of the drivers’ suspensions might just loosen up a little. I think this is more likely than the former to be audible. But, I think both of these factors are likely to pale into insignificance in comparison with the adaptation of our auditory perception, to transducers with a new sound signature. Our perception is extremely good at not hearing things that are interpreted unconsciously as noise, or “non-signal”, for example, the clatter of plates and cutlery, & the chatter of other diners, in a restaurant. Take a recording in that environment and play it back in a quiet environment and you will immediately notice what you had not noticed when you were there. Thus, speakers may appear to lose excessive sibilance as we adapt to them. Similarly, our auditory system is incredibly good at filling in the missing components of music that we expect to be hearing. This is one of the reasons that some small speakers appear to have such amazing bass; they reproduce the higher harmonics of the fundamental frequencies accurately, so even if the fundamental frequencies are barely audible it will sound to us as if they are.
To those who swear that breaking in must be real because their speakers sound better after playing for days without listening to them, I ask this. How do you separate your perception from your expectations? I don’t think this is actually possible. Anyone who leaves their speakers playing in another room without listening to them for weeks is, in my opinion, very likely to have high expectations that breaking in will improve them. Otherwise, why bother? And so, they now sound better to you. Placebo response is measured in clinical settings and demonstrated to have very significant effect. Don’t underestimate it! Want to eliminate it? Do a randomised double blind control trial. If you want to know how to design such a trial, ask me. This post is too long already.
My advice? Don’t sweat it. If your system sounds better after some time, just be grateful. But it it sounds horrible on demonstration in the store, don’t buy it with the expectation that it will improve significantly. If it sounds worse over time you need to upgrade, very carefully.
I ask you; If breaking in is as significant, as some claim, then how come it’s not been measured? If anyone knows of such Objective measurements, then please enlighten me.
Enjoy your new old speakers. If they get better as you listen to them, then that’s wonderful, but don’t fuss about how that is happening. It’s probably your amazing brain doing what it evolved to do; perceiving, not just hearing.